Giant magnetoresistance (GMR) elements composed of a multilayer film of ferromagnetic layers and non-magnetic layers, and tunnel magnetoresistance (TMR) elements which use insulating layers (tunnel barrier layers, barrier layers) for the non-magnetic layers are already known. Generally, although TMR elements have a higher element resistance than GMR elements, the magnetoresistance (MR) ratio of TMR elements is larger than the MR ratio of GMR elements. Consequently, TMR elements are attracting much attention as elements for magnetic sensors, high-frequency components, magnetic heads and non-volatile random access memory (MRAM).
Examples of known methods for writing to MRAM include a method in which a magnetic field generated by an electric current is used to perform writing (magnetization rotation), and a method in which a spin transfer torque (STT) generated by passing an electric current through the stacking direction of a magnetoresistance element is used to perform writing (magnetization rotation).
In the method that uses a magnetic field, a problem arises in that when the size of the element is small, writing becomes impossible to perform with the size of the electric current that is able to flow through the fine wires.
In contrast, in the method that uses spin transfer torque (STT), one ferromagnetic layer (the fixed layer or reference layer) causes spin polarization of the current, that current spin is transferred to the magnetization of the other ferromagnetic layer (the free layer or recording layer), and the torque (STT) generated at that time is used to perform writing (magnetization rotation), and this method offers the advantage that as the size of the element decreases, the size of the current required for writing also decreases.